If the fuel pump doesn't "prime" when you turn the key on, it could be a bad
relay or the wrong relay. Also, make sure to tell the parts guy if you have
a 5-cyl or 4-cyl engine when ordering. Just saying "4000" isn't enough.
The relay has a built in rev limiter which is matched to the engine.
Install the 4-cyl relay in a 5-cyl car and you hit a brick wall around 4000
rpm. That's no fun :-)
Peter Lines